The present invention relates to the forming of materials by extrusion.
U.S. Pat. Application Ser. No. 228,673 which has been assigned to the present Assignee discloses and claims an extrusion apparatus which comprises first and second members defining an elongate passageway therebetween, said first and second members being movable one relative to the other in the direction of the length of the passageway, an abutment member fixed relative to the second member projecting into and blocking the passageway, means defining at least one die orifice leading from the passageway adjacent the abutment member, said orifice extending from said passageway to a point outside said apparatus whereby material fed to said apparatus is extruded therethrough, means for continuously feeding material to be extruded from a position outside said apparatus into said passageway at a point spaced from the abutment member, the amount of the surface area of the passageway defined by the first member which is movable towards the abutment member being greater than the amount of the surface area of the passageway defined by the second member, whereby material fed into the passageway is moved by frictional drag with the surfaces of the passageway in the first member towards the abutment member and is thereby extruded through the die orifice.
The passageway can be formed by an endless groove in the first member with the second member being in the form of a shoe covering a part of the length of the groove. The shoe is positioned as close as possible to the first member and over the groove in the first member.
Conveniently the first member can be a wheel member and preferably the endless groove is formed in the peripheral edge of the wheel member.
Experience has shown that the wheel member can develop fatigue failure arising from fluctuating stresses therein upon rotation of the wheel member to extrude material. The stresses reach a maximum in that portion of the wheel member immediately in front of and adjacent the abutment member, falling to a minimum in that portion of the wheel member to the rear of the abutment member. This continued stress cycling during rotation of the wheel member can eventually result in failure and fracture of the wheel member.